Gene-Culture Coevolution

Evolution: Differential transmission of genes Cultural Evolution: Differential transmission, via social learning, of cultural traits

Gene-culture coevolution How might genetic and cultural evolution interact? When correlate, when oppose? Can cultural transmission alter selection pressures? Given social learning, can population genetic structure influence rates of cultural transmission?

Gene-culture coevolution Can what an individual learns depend on its genotype? Can natural selection on gene frequencies be generated by, be modified by, spread of a cultural trait?

Gene-culture coevolution Gene-culture theory Individual: genotype & cultural trait “Phenogenotype” dynamics: Mendelian inheritance & cultural transmission

Gene-culture coevolution Feldman & Laland Gene-culture coevolutionary theory. Trends Ecol. Evol. 11:453.

Gene-culture coevolution Cultural transmission can modify selection pressures, alter evolution Selection differs by presence/absence of cultural trait Dairy farming: lactose digestion

Dairy farming Energy-rich sugar lactose (milk sugar) Lactase: Enzyme activity, digest lactose Otherwise: Illness (Cheese, yogurt)

Dairy farming Dairy farming Lactose absorption Adults: variation in milk digestion Among-populations Lactose absorption strong genetic basis Dominant autosomal trait Many, but not all, populations: Only 20% adults digest milk

Dairy farming Note correlation: lactose absorption & history of dairy farming Culture: Dairy, Important app YBP Gene: Absorbers 90% of adults, Why allele so common in population with history of milk consumption?

Dairy farming Dairy farming culture: selective pressure for milk digestion ? Adsorption allele A vs a (Non-absorb) Two cultural states (use, not-use milk) 6 phenogenotypes Assume Vertical cultural transmission only Fitness advantage milk digestion

Dairy farming Advance of adsorption allele depends Strong enough cultural transmission Fitness advantage milk use 1. Culture: Use-milk transmits use-milk 2. Lactose adsorption increases survival

Dairy farming Milk use does not always spread, despite fitness advantage Culture can inhibit selection favoring adsorption allele: Dairy farming not transmitted, Individual cannot gain lactose survival

Lactose absorption Must combine allele A and milk-use culture to gain (assumed) fitness advantage. Critical cultural transmission fidelity to promote allele, for given fitness advantage Interaction of 2 modes inheritance: Gene-culture coevolution

Natural selection may oppose culture Excess female mortality Preference for sons in some areas Cultural attribute Greater female mortality before age first reproduction

Excess female mortality Gene: SRVX, “femaleness” gene Distorts sex ratio in humans Can cultural bias favoring sons influence selection on sex-ratio distorter gene ?

Excess female mortality Model: Cultural  sons > daughters Know (sex-ratio evolution): Increased fitness female offspring Rarer sex has more mean offspring Gene for daughters > sons favored

Excess female mortality N-person game equilibrium: IF parents have more children to compensate for lost daughters: Female-bias in sex ratio at birth compensates for cultural bias favoring males Adult sex ratio unbiased

Excess female mortality IF parents have more children to compensate for lost daughters: Adult sex ratio unbiased: Additional births allow natural selection favoring allele for female biased sex ratio at birth

Excess female mortality Other cultural practices: adjust sex ratio & number of offspring Can bias primary sex ratio toward males Culture profoundly affects evolution of sex-ratio gene

Gene-culture coevolution Horizontal cultural transmission may promote group selection in some environments May counter individual selection within groups Conformism: new model human altruism?